Flame photometric detector employing premixed hydrogen and oxygen gases

ABSTRACT

A flame photometric detector including a burner assembly having a first passageway leading to the burner tip so that a mixture of the hydrogen fuel gas and the combustion supporting gas such as oxygen may be delivered via the passageway to the burner tip to produce a hydrogen rich reducing flame. The sample to be analyzed is delivered via a second passageway and directed by a sample guide to the peripheral region of the reducing flame where the sample is burned in a relatively low temperature, hydrogen rich region whereby the interfering light emission from interfering substances is maintained at a low level.

United States Patent [1 1 Delew [111 3,879,126 1 1 Apr. 22, 1975 FLAMEPHOTOMETRIC DETECTOR EMPLOYING PREMIXED HYDROGEN AND OXYGEN GASES [75]Inventor: Richard Brandt-Delew,Corte 21 Appl. No.: 389,614

Related U.S. Application Data [63] Continuation of Ser. No. 232.926,March 8, 1972,

abandoned.

[52] U.S. Cl 356/87; 431/126 [51] Int. Cl. G0lj 3/30 [58] Field ofSearch 356/87, 187; 431/126 [56] References Cited UNITED STATES PATENTS2,714,833 8/1955 Gilbert 356/87 UX 2,836,097 5/1958 Garman 356/87 X2.990.749 7/1961 Theirs et 356/87 UX 3.586.446 6/1971 Findl ct a1 356/87OTHER PUBLICATIONS Analytical Flame Spectroscopy, edited by R.Mavrodineanu, MacMillian and Co., London, 1970, pp. 238-249; 256-267;278-283; 285-295; 358-363; 366-373. Gaydon et al., The Spectra of FlamesContaining Oxides of Sulfur, Proc. Roy. Soc. A189, 1947, pp. 313-325.

Brite, Flame Photometry of Organic Phosphorus, Analytical Chemistry,Vol. 27, No. 11, November 1955.

Societe Chimique de France, Bulletin, Vol. 13, pp. 289 and 290, (1890).

National Instrument Laboratories, Inc., Bulletin 4-7006, The N.l.L.Digital Flame Photometer, printed May 1968.

Primary E.\'aminerRonald L. Wibert Assistant Examiner-F. L. EvansAttorney, Agent, or Firm-Stanley Z. Cole; Gerald M. Fisher; John J.Morrissey [57] ABSTRACT A flame photometric detector including a burnerassembly having a first passageway leading to the burner tip so that amixture of the hydrogen fuel gas and the combustion supporting gas suchas oxygen may be delivered via the passageway to the burner tip toproduce a hydrogen rich reducing flame. The sample to be analyzed isdelivered via a second passageway and directed by a sample guide to theperipheral region of the reducing flame where the sample is burned in arelatively low temperature, hydrogen rich region whereby the interferinglight emission from interfering substances is maintained at a low level.

6 Claims, 3 Drawing Figures FLAME PHOTOMETRIC DETECTOR EMPLOYINGPREMIXED HYDROGEN AND OXYGEN GASES This is a continuation of applicationSer. No. 232.926 filed 3/8/72. now abandoned.

BACKGROUND OF THE INVENTION Flame photometric detectors are now incommon use as relatively inexpensive spectroscopic detectors for usewith gas chromatographs. particularly for the analysis of sulfur andphosphorus substances in the effluent from the gas chromatograph. Asdescribed in an article entitled Gas Chromatographic Detectors" by C. H.Hartmann in Analytical Chemistry. Vol. 43. No. 2, pages 113A to 125A.February I971. the basic elements of the flame photometric detectorinclude a burner jet where the sample of effluent from the GC is burnedor heated in the combustion provided by H fuel gas and a combustionsupporting gas such as oxygen or air. and a spectrophotometer forobserving the sample including a suitable light filter andphotodetector. When substances containing sulfur are brought intocontact with the hydrogen rich flame. they emit a characteristic lightspectrum at about 360-410 nm; phosphorus-containing substances producelight emission centered about 526 nm.

In the known form of such detectors as illustrated by the structuresshown in U.S. Pat. No. 3.290.] 18 issued Dec. 6. I966 to C. Van DerSmissen entitled Appara- I tus For Detecting Phosphorus And/Or Sulfur inGases" and U.S. Pat. No. 3.489.498 issued .Ian. 13. I970 to S. Brody etal entitled Flame Photometric Detector With Improved Specificity ToSulfur And Phosphorus." the sample under test. for example air or thecolumn effluent from a gas chromatograph mixed with the combustionsupporting gas such as oxygen or air, is delivered to the burner tipthrough a first tube or passageway. The hydrogen is delivered to theburner housing via a separate passageway where it burns with the samplegas and oxygen and produces the desired combustion.

The flame produced by such a device may not be reliable in operationsince. for example. it is subject to blowout resulting from a suddensurge of solvent in the effluent from the chromatograph and a resultantoxygen starvation. In addition. should the column output including theoxygen source be disconnected from the detector input. the flame isextinguished and the hydrogen may escape and create a safety hazard.

Additionally. when the sample and carrier gas are fed into the very hotcenter portion of the hydrogen and oxygen flame. the burning ofsubstances such as organic compounds which may be present results in aninterfering light emission. reducing the specificity of the detector.i.e.. the ability to respond primarily to a select group or groups ofsubstances with a minimal response to all other substances. Specialefforts have been employed in the past in an effort to block thisinterfering light emission from the spectrophotometer; for example. inU.S. Pat. No. 3.489.498 a cylindrical shield is provided about the tipof the burner so that the lower portion of the flame where suchinterferenceproducing burning normally takes place is not in the opticalline of sight of the photospectrometer so that such interfering lightemission will not degrade the selectivity. However. blocking the emittedlight in this fashion tends to reduce detector sensitivity. i.e.. theeffectiveness of the detector as a transducer in converting the sampleinto a measurable electrical signal. since it also blocks a portion ofthe desired emission.

SUMMARY OF THE PRESENT INVENTION The present invention providesa novelflame photometric detector wherein the hydrogen fuel gas and thecombustion supporting gas, e.g.. oxygen. are premixed and then deliveredto the burner tip via one passageway to produce the desired reducingflame at the tip. The sample is delivered to the peripheral region ofthe flame via a separate passageway such that contact of the sample andthe flame occurs in the outer portion of the flame. As a result, theflame is considerably more reliable and not snuffed out with surges ofsolvent through the sample conduit. In fact, the flame continues evenwhen the gas chromatograph column is removed. As a consequence of thispremixing there is no free flowing hydrogen to escape.

Since the sample is introduced into the peripheral re gion of the flame,it is burned or heated in a cooler por-' tion of the hydrogen-rich flameand this results in the substances of interest being burned or heated atoptimum conditions, includingtemperature and hydrogen concentration.while at the same time the interfering substances are being burned orheated at non-optimum conditions for them. This results in minimuminterfering light emission. and thus a more encompassing view of theflame may be provided to the spectrophotometer.

DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal cross section viewof a preferred form of flame photometric detector structure of thepresent invention.

FIG. 2 is an enlarged view of the tip region of the burner assemblyregion of FIG. 1. and

FIG. 3 is a response curve for a prior art detector and the detector ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings.the detector comprises a generally elongated body structure includingthe burner means 11 mounted in one end thereof. the photospectrometerstructure 12 mounted in the opposite end thereof. and the combustionchamber 13 positioned therebetween. As with standard forms of flamephotometric detectors. the structure is provided with a suitable igniterassembly 14 for igniting the flame and an ion collector means 15, formonitoring hydrocarbons within the chamber 13.

The burner means comprises a mounting base 21 having a threaded bore 22therein and a cylindrical burner base 23 threaded into the bore in themounting base. The burner base 23 is provided with an axial bore 24therein. the bore being internally threaded at itstop end and taperingdown into a smaller diameter bore 24' near the lower end where it isprovided with a flow passage bore 25. This bore 25 mates with a bore 26leading out through the mounting base 21 to a T connection tubing 27 thetwo branches of the tubing being fed via control needle valves 28 and 29from the sources of hydrogen and oxygen, respectively.

A burner tip assembly is mounted in the bore within the burner base andcomprises a hollow cylindrical flame tip member 31, a brass ferule 32.and a hollow cylindrical nut 33 forming a sample guide member. The

hollow cylindrical flame tip member 31 is nested at one end into thelower end of the bore 24 in the burner base 23, the flame tip memberbeing engaged by the annular ferule 32 which is urged downwardly againstthe outer wall of the flame tip member 31 and the inner wall of theburner base 23 by the hollow cylindrical sample guide 33 threaded intothe bore in the burner base. A bore 34 extends through the burner base23 from the lower end thereof this bore mating with a bore 34' in thebase 21 where it connects with a conduit 35 serving as the sample input.The bore 34 leads into the annular chamber 36 formed between the innerwall of the sample guide 33 and the outer wall of the flame tip member31. The sample guide 33 is provided with notches 33' in its threadedinner end to provide good ingress from the bore 34 to the annularchamber 36.

ln operation. the hydrogen fuel gas and the combustion supporting gas.i.e., oxygen, are delivered via the needle valve controls 28 and 29 tothe flow passage tubing 27 where they are mixed and then brought intothe bore 26 in the mounting base. passing up through the central bore inthe flame tip member 31 to the end of the tip member where the gases areignited by a suitable flame igniter 14 to form the hydrogen-rich flame.The sample including the carrier from the chromatographic column isintroduced through the bore 34 in the lower end of the burner base 23and passes around the upper portion of the ferrule 32 and into thechamber 36 surrounding the flame tip 31. The sample is then directed bythe sample guide 33 into the peripheral region of the reducing flame.i.e., the lower temperature hydrogen-rich region. The temperature ofthis region is in the order of 400C as distinguished from thetemperature in the oxidation region of the flame of the order of l.700C.While burning or heating of the substances of interest is optimized atthis hydrogen-rich 400 C region to give good light emission therefrom.the undesired interference substances, such as hydrocarbons. are notburned efficiently. Thus, the interfering light emissions are maintainedat a relatively low value.

The photospectrometer unit 12 comprising the standard photomultipliertube 41. light filter 42, and explosion shield 43 are positioned aboveand in axial alignment with the axis of the burner assembly to give afull end-on viewing of the flame in accordance with the teachings of theU.S. Patent application of C. Hartmann filed concurrently herewith andentitled Flame Photometric Detector With End-On Flame Viewing. It shouldbe understood that the combustion region may also be viewed from theside as with the standard existing forms of photometric flame detector.and the benefit of lower interfering emissions stemming from theimproved burner design will still be obtained.

Referring to FIG. 3 there is shown two curves representing the flamephotometric detector response in amps for a standard known form ofdetector. curve A. and the detector employing the heater of the presentinvention, curve B. obtained with different steady state levels ofsulfur dioxide burned as the sample. Although the response is higher forthe detector described herein a higher noise level was also obtained sothat the net detectivity of the two devices is about the same. While theprior art detector A exhibits a limit to dynamic range at about ppm, thedetector described herein has a dynamic range reaching at least to 50ppm.

The novel combination of the burner assembly of this invention with theend-on spectrophotometer viewing technique of the above cited C.Hartmann application is shown and described in a U.S. Patent applicationfiled concurrently herewith by R. DeLew and C. Hartmann entitled FlamePhotometric Detector Employing Premixed Hydrogen and Oxygen Gases forSample Combustion With End-On Spectrophotometer Viewing of The Flame."

What is claimed is:

1. Flame photometric detector apparatus comprising burner means;

a first conduit for connection to a source of selfcombustible gas, saidself-combustible gas being a mixture of a fuel gas and a combustionsupporting gas. said self-combustible gas being capable of supportingcombustion without addition of any further gases;

a second conduit for connection to a source of sample material to beanalyzed;

said burner means including a flame tip, said flame tip having aself-combustible gas outlet. said burner means further including a firstpassageway and a second passageway. said first passageway beingconnected between said first conduit and said flame tip self-combustiblegas outlet. said second passageway being separated from said firstpassageway and being connected to said second conduit, said secondpassageway having an outlet radially displaced from saidself-combustible gas outlet for delivery, in operation. of said sampleto the cooler side peripheral region of a flame, and

a photodetector means adopted to receive, in operation of said system.photoemission from said sample for qualitative and quantative detectionof said sample.

2. The flame photometric detector as claimed in claim I wherein saidsecond passageway includes a sample guide member surrounding thecombustible gas outlet of said flame tip for bringing sample intocontact with the cooler side peripheral regions of said flame.

3. A flame photometric detection process for detecting the presence ofselected substances in a sample comprising the steps of mixing a fuelgas with a combustion-supporting gas to form a hydrogen-rich mixed gasand continuously discharging said hydrogen-rich mixed gas from a flametip and burning said discharged gas thereby producing a reducing flame,

delivering a sample to the cooler side peripheral region of saidreducing flame.

and viewing the flame zone with a spectrophotometer.

4. A process as claimed in claim 3 wherein said fuel gas is hydrogen.

5. A process as claimed in claim 3 wherein said mixed gases comprise ahydrogen-rich mixture of hydrogen and oxygen.

6. A process as claimed in claim 3 wherein the step of delivering asample to the cooler peripheral region includes continuously deliveringa carrier gas to said cooler peripheral region. said carrier gas movingsaid sample into said cooler region.

1. Flame photometric detector apparatus comprising burner means; a firstconduit for connection to a source of selfcombustible gas, saidself-combustible gas being a mixture of a fuel gas and a combustionsupporting gas, said self-combustible gas being capable of supportingcombustion without addition of any further gases; a second conduit forconnection to a source of sample material to be analyzed; said burnermeans including a flame tip, said flame tip having a self-combustiblegas outlet, said burner means further including a first passageway and asecond passageway, said first passageway being connected between saidfirst conduit and said flame tip self-combustible gas outlet, saidsecond passageway being separated from said first passageway and beingconnected to said second conduit, said second passageway having anoutlet radially displaced from said self-combustible gas outlet fordelivery, in operation, of said sample to the cooler side peripheralregion of a flame, and a photodetector means adopted to receive, inoperation of said system, photoemission from said sample for qualitativeand quantative detection of said sample.
 1. Flame photometric detectorapparatus comprising burner means; a first conduit for connection to asource of selfcombustible gas, said self-combustible gas being a mixtureof a fuel gas and a combustion supporting gas, said self-combustible gasbeing capable of supporting combustion without addition of any furthergases; a second conduit for connection to a source of sample material tobe analyzed; said burner means including a flame tip, said flame tiphaving a self-combustible gas outlet, said burner means furtherincluding a first passageway and a second passageway, said firstpassageway being connected between said first conduit and said flame tipself-combustible gas outlet, said second passageway being separated fromsaid first passageway and being connected to said second conduit, saidsecond passageway having an outlet radially displaced from saidself-combustible gas outlet for delivery, in operation, of said sampleto the cooler side peripheral region of a flame, and a photodetectormeans adopted to receive, in operation of said system, photoemissionfrom said sample for qualitative and quantative detection of saidsample.
 2. The flame photometric detector as claimed in claim 1 whereinsaid second passageway includes a sample guide member surrounding thecombustible gas outlet of said flame tip for bringing sample intocontact with the cooler side peripheral regions of said flame.
 3. Aflame photometric detection process for detecting the presence ofselected substances in a sample comprising the steps of mixing a fuelgas with a combustion-supporting gas to form a hydrogen-rich mixed gasand continuously discharging said hydrogen-rich mixed gas from a flametip and burning said discharged gas thereby producing a reducing flame,delivering a sample to the cooler side peripheral region of saidreducing flame, and viewing the flame zone with a spectrophotometer. 4.A process as claimed in claim 3 wherein said fuel gas is hydrogen.
 5. Aprocess as claimed in claim 3 wherein said mixed gases comprise ahydrogen-rich mixture of hydrogen and oxygen.